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Failing duct smoke

TheCommish

TheCommish

SAWHORSE
Joined
Sep 27, 2011
Messages
2,182
Location
Charlton Ma
We have a sewer treatment plant in town and it has enclosed treatment space that is humid but cool. To keep the air quality up (it stinks a little) the is a MAU about 100,000 btu with a very large fan (over 2000 cfm) to blow heated clean air into one end of the building, with a number of exhaust fans around the perimeter to exhaust the stale air.

Given the fan is over 2000 cfm there is a dust smoke detector and given that heating fuel is expensive the heat is turned on sparingly, however the fan runs automatically to change over the air in the building.

We are now having problems the duct smoke detector alarming mostly due to condensation in the duct system and into the detector affecting the electronics of the detector.

Does anyone have cost effective (cheep) solution to the problem? The alarm company is looking into a weather proof duct smoke, that seems to be set up for outdoor duct use. I have suggested a beam type smoke detector across the 60 foot output diffuser area.
 
Why is the detector required in the first place.

If all it is only a fan?

Do you have a code secretion for the requirement

Do no think you will find a smoke that will work in that environment

A beam is an expensive cost
 
Seems like you can use the exception , but do not feel a smoke is require on a fan

606.2 Where required. Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.
 
AIR DISTRIBUTION SYSTEM. Any system of ducts, plenums and air-handling equipment that circulates air within a space or spaces and includes systems made up of one or more air-handling units.

SECTION 606 SMOKE DETECTION SYSTEMS CONTROL

606.1 Controls required. Air distribution systems shall be equipped with smoke detectors listed and labeled for installation in air distribution systems, as required by this section. Duct smoke detectors shall comply with UL 268A. Other smoke detectors shall comply with UL 268.
 
Exception Number Two:

​
“Fan units whose sole function is to remove air from

​
inside the building to outside the building.” (NFPA

​
90A, 2002, 6.4.2.3)

 
it is an incoming air unit and I am aware of the need for smoke detection required by NFPA 90A which is in play here, what I am looking for is alternative detector or method suit for damp environment
 
TheCommish said:
it is an incoming air unit and I am aware of the need for smoke detection required by NFPA 90A which is in play here, what I am looking for is alternative detector or method suit for damp environment
Click to expand...
Is it a plain fan or is it a air handler?
 
TheCommish said:
it is an incoming air unit and I am aware of the need for smoke detection required by NFPA 90A which is in play here, what I am looking for is alternative detector or method suit for damp environment
Click to expand...
And why doesn't the exception apply?? If it is an air handler

shall be installed where indicated in Sections 606.2.1 through 606.2.3.

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.
 
from 72::

17.7.1.8* Unless specifically designed and listed for the expected conditions, smoke detectors shall not be installed if any of the following ambient conditions exist:

(1)

Temperature below 32°F (0°C)

(2)

Temperature above 100°F (38°C)

(3)

Relative humidity above 93 percent

(4)

Air velocity greater than 300 ft/min (1.5 m/sec)

This also applies to the smoke detector used for the duct detection
 
Last edited by a moderator:
NFPA 90A is a Massachusetts state refrence, we do not use the IFC here

Interesting 17.7.1.8* Unless specifically designed and listed for the expected conditions, smoke detectors shall not be installed if any of the following ambient conditions exist:

What edition of NFPA72
 
Last edited by a moderator:
This is out of the IMC which mass has adopted;;

The exception should apply

606.2 Where required. Smoke detectors shall be installed where indicated in Sections 606.2.1 through 606.2.3.

Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.
 
cda said:
2010More than likely same in earlier editions

Appears mass has adopted IMC

http://www.mass.gov/eopss/consumer-prot-and-bus-lic/license-type/csl/8th-edition-base-code.html
Click to expand...
It is in the 1996 edition:::

5-3,6.1.!* Smoke detectors shall be installed in areas

where the normal ambient conditions are not likely to

exceed the following range of environmental conditions:

(a) A temperature of 100°F (38°C), or a temperature 32°F

(0°C); or

(b) A relative humidity of 93 percent; or

© An air velocity of 300 fpm (1.5 raps).

Exception: Detectors specifically designed for use in ambients

exceeding the limits of 5-3.6.1.1(a) through © and listed for the

temperature, humidity, and air velocity conditions expected.
 
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